The use of polyester polymers and their application in coatings compositions is well known in the art. Coatings utilizing polyester polymers can be advantageous over coatings with polyurethane and acrylic polymers for one or two basic reasons. Polyester polymers have the benefit of lower cost and lower volatile organic content (VOC) and depending on the required application have good durability, adhesion and appearance.
Even with these benefits, polyester containing coatings are more difficult to formulate at lower VOC's and higher solids while maintaining film properties. The desired film properties occur with the use of the higher molecular weight polyester polymers (on the order of 3500 to 5000 weight average molecular weight). The higher molecular weights also lead to increased VOC's and a lower paint solids which are undesirable environmentally.
It would be desirable to utilize polyester polymers which would be low in cost, higher in coating solids, lower in VOC while achieving the desired film properties such as adhesion. In addition, for automotive coatings, there is a need for a coating which will provide good durability, improved adhesion and lower VOC, especially during two-tone paint applications where a clearcoat may be directly applied to a primer or primer-surfacer layer.